1. Field of the Invention
The present invention generally relates to a wavelength calibration method and a wavelength calibration apparatus.
Priority is claimed on Japanese Patent Application No. 2006-041082, filed Feb. 17, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Japanese Unexamined Patent Application, First Publication, No. 2000-283841 discloses a conventional wavelength calibration technique to be used in an optical spectrum analyzer. This conventional wavelength calibration technique will be described as follows. A light emitting diode is performed as a reference light source to emit a reference light with a predetermined wavelength band toward a gas absorption cell. The gas absorption cell causes light absorptions at particular wavelengths that correspond to reference wavelengths, thereby obtaining an observed spectrum. The observed spectrum indicates absorption wavelengths as observation wavelengths.
The absorption wavelengths as observation wavelengths are then compared to the above-described particular wavelengths as reference wavelengths to detect a difference as an error between them at each wavelength. The wavelength calibration of the optical spectrum analyzer is performed based on the average of the detected errors for the particular wavelengths. If the absorption wavelengths as observation wavelengths are identical to the particular wavelengths as reference wavelengths, this means that the wavelength measured by the optical spectrum analyzer has no error. If the absorption wavelengths are different from the particular wavelengths, this means that the measured wavelength has an error. The wavelength calibration of the optical spectrum analyzer is performed so that the absorption wavelengths as observation wavelengths become identical to the particular wavelengths as reference wavelengths.
The above-described conventional wavelength calibration technique performs the wavelength calibration based on the average of plural errors at plural particular wavelengths, thereby further reducing the calibration error. Namely, the above-described conventional wavelength calibration technique can improve the accuracy of wavelength measurement as compared to another conventional technique that performs wavelength calibration based on an error at a single particular wavelength.
Further, the wavelength calibration can be performed by using the light emitting diode as a light source. It has been well known that the light emitting diode includes a semiconductor chip disposed between an anode and a cathode. The light emitting diode may cause an interference of the emitted light in the semiconductor chip. The interference of the emitted light may cause a ripple in intensity of the emitted light in the wavelength band. The ripple may cause errors of the absorption wavelengths.
The light emitting diode may have an overall unevenness or non-flatness of the light intensity distribution in the wavelength band. The overall unevenness of the light intensity distribution may cause further errors of the absorption wavelengths.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.